Most semiconductor manufacture processes comprise diffusion, ion implantation, and deposition, etching and cleaning. Particularly, the deposition process uses a large amount of reaction gas such as TMGa, NH3 and H2. After having been reacted within the chamber, a part of the gas forms products on the substrate (such as a wafer) and another part remains unreacted and forms exhaust which must be discharged from the chamber.
Let the reactor used in the chemical vapor deposition be taken for example. The reaction gas is mainly provided via feeding openings disposed above the substrate. The feeding openings vertically face a surface of the substrate, such that the reaction gas flows outwards from the center of the susceptor which supports the substrate and forms products on the surface of the substrate and the unreacted gas flows to the discharge opening from outer sides of the susceptor to be discharged from the chamber. The discharge opening is disposed under the susceptor. The channel design of reactor with the reaction gas being fed via the top and discharged via the bottom has following disadvantages. Since the reaction gas flows towards the peripheral area from the center of the susceptor, concentration and mass flow rate of the reaction gas both decrease along flowing direction, causing products to have a higher deposition rate at the center of the susceptor than at the peripheral area of the susceptor.